Euphausiid harvesting and processing method and apparatus

ABSTRACT

Method and apparatus for harvesting and processing zooplankton and, in particular, for harvesting and processing euphausiids for subsequent use as a feed product for early stage juvenile or larvae feed or for a food product as an additive. The euphausiids are continuously harvested from coastal waters and dewatered. The dewatered product is passed to a heat exchanger to increase its temperature and, thence, to a digester where a desired level of enzymatic activity is obtained. The product is then held by a surge tank for subsequent transfer to a ball dryer where the product is dried at a relatively low temperature without destroying the stabilized enzymes created in the digester. The digesting step may be deleted in the event the end use of the product is for a food product.

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/202,593 filed Feb. 28, 1994. This application is acontinuation of U.S. patent application Ser. No. 08/386,507 filed Feb.10, 1995 now abandoned.

INTRODUCTION

This invention relates to a method and apparatus for harvesting andprocessing zooplankton and, more particularly, to a method and apparatusfor harvesting and processing euphausiids into a food products for humanconsumption such as for a carotenoid containing food product and/or intoa feed products for animal consumption including aquaculture especiallyrelating to juvenile fish culture.

BACKGROUND OF THE INVENTION

With the advent of increasing activity in aquaculture or fish farming inthe early to mid-1980s, research has been ongoing into increasingproductivity or growth rate and reducing the mortality rate of fishraised in aquaculture conditions since survival of such fish isimportant. One such factor relates to enhancing the nutritional valueand palatability of feed used in raising such fish. In addition to thenutritional value, it is desirable to reduce the cost of feed to suchfish since, typically, the feed totals approximately 40 to 50% of thecost of raising the fish. Such feed should be a high quality feed tomeet the objectives of having high nutritional value to maximize growthand to reduce fish mortality.

The requirement for feed products in aquaculture is projected to growsubstantially and, as a result, there is and will be pressure to obtainthe necessary ingredients for fish food. The possibility of usingzooplankton and, in particular, euphausiids, as a fish feed, appetizeror food product has been investigated and has been found to be possibleand desirable, particularly as a feed product. Euphausiids are a naturalfeed harvested directly from coastal waters and have a high nutritionalvalue but, previously, the cost of harvesting and processing suchzooplankton for a feed product has been prohibitively expensive.

As well, the questions of the availability of the biomass of suchzooplankton, storage of the zooplankton and its harvesting andprocessing are parameters that must be investigated in order todetermine whether the product would be appropriate as a feed product.

Through papers written by Fulton and other authors, the use ofzooplankton as a food or feed product has been contemplated for sometime. In particular, antarctic krill (Euphausia superba) for humanconsumption have been investigated, although relatively little work hasbeen investigated related to aquaculture. The use of Euphausia pacificain the coastal waters of British Columbia, Canada has been considered inrelation to aquaculture only.

It appears, from those investigations, that the necessary biomass isavailable in coastal waters. Previously, euphausiids have been used as apet food ingredient and some aquaculture operators have used euphausiidsas a feed product. The euphausiids were used for such purposes in afrozen form after being harvested and in some cases, the euphausiidswere freeze dried following harvesting. This is an expensive procedure.

Harvesting euphausiids from coastal waters was previously done utilizinga mid-water trawl. When the trawl net was full of euphausiids, the trawlnet would be raised and the euphausiids would be stored on a shipboardlocation for subsequent freezing. In utilizing the mid-water trawl net,however, severe damage was caused to the euphausiids by being bunched inthe cod end of the net. The euphausiids would end up being squashed andleaching action would occur when the net was raised which is believed toreduce the nutritional value of the euphausiids. To reduce this damage,only a certain weight of euphausiids were subsequently taken in eachoperation when raising the net in an attempt to reduce the handlingdamage. Nevertheless, a certain degree of damage still occurred and, ofcourse, the time required to raise the net is a disadvantage because ofthe reduction of fishing time.

In processing feed products, it has typically been the case that theingredients used in such feed products are heated to a high temperaturearound 100° C. when the product is processed and dried. By heating theproduct to such a high temperature, it is believed that the enzymes andother proteins in the product are denatured. If, however, it is intendedto utilize the product for early stage or juvenile aquaculture, whichyoung fish have relatively undeveloped digestive systems, it is believedto be desirable that the euphausiids maintain a certain proportion ofenzymes which will assist the digestive process in such larvae. If thetheory that enzymes are advantageous in nutrition is correct, suchdestruction of the enzymes during the aforementioned drying process isdisadvantageous.

It is also desirable to have a natural product, where the proteins arenot denatured, available for early stage juvenile or larvae feed. Insome previous products, exogenous enzymes have been added to thezooplankton mix. However, the addition of such enzymes is difficult tocontrol and can result in a complete hydrolysis of the proteins to aminoacids. The presence of free amino acids in the feed needs to becontrolled since they can create an inferior product of substantiallyreduced value for a feed product.

It has been shown, surprisingly, that the degree of enzyme activitywhich results in determining the digestibility of a product, reaches arelatively constant value after a certain period of time in a naturalproduct. Recent investigations conducted by the applicant have confirmedthis characteristic for Euphausia pacifica. This characteristic wasfirst discovered in relation to Euphausia superba by Kubota and Sakai ina report entitled "Autolysis of Antarctic Krill Protein and ItsInactivation by Combined Effects of Temperature and pH", Transactions ofthe Tokyo University of Fisheries, number 2, page 53-63, March 1978.However, the antarctic krill study done by Messrs. Kubota and Sakai hadthe objective of limiting enzyme activity which was deleterious toobtaining a food as opposed to a feed product. Messrs. Kubota and Sakaiwished to inhibit the enzymatic activity by certain processingtechniques which they considered desirable when the product was intendedas a food product.

When a degree of stabilization in enzymatic activity has been obtainedduring the digestive process in the euphausiids, further processing maytake place in order to make a useful product for commercial feed. Suchprocesses may include adding acid to obtain an acid stabilized productor drying the product using a variety of drying techniques such asfreeze drying, spray drying, or vacuum and air drying. Spray drying, aswell as other drying processes, however, are done at temperatures thatwill permanently inactivate the enzymes in the euphausiids which, asearlier mentioned, is considered to be undesirable for aquaculturepurposes although it is acceptable for purposes where the product isintended to be used as a carotenoid biopigment for coloring purposes inboth feed and food products.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided a method ofharvesting zooplankton comprising towing a trawl net behind a vessel incoastal waters through a location of zooplankton, said net having anopen forward end and a rearward cod end, means to maintain said open endof said net at a predetermined depth below the surface of said coastalwaters where said zooplankton are located, a cage positioned in said codend of said net to maintain said cod end in an open condition and a pumpto continuously remove said zooplankton from said cod end of said netand to move said zooplankton to a shipboard location.

According to a further aspect of the invention, there is providedapparatus for harvesting zooplankton from coastal waters comprising atrawl net having an open end and a rearward cod end, means to pull saidtrawl net behind a towing vessel, means to maintain said open end ofsaid trawl net at a predetermined depth below the surface of saidcoastal waters, means to maintain said cod end of said net in an opencondition and means to pump said zooplankton from said cod end of saidnet to a shipboard location.

According to yet a further aspect of the invention, there is provided amethod of producing a feed product comprising heating a quantity ofzooplankton to a predetermined temperature less than 70° C., maintainingsaid temperature for a predetermined time period uniformly throughoutsaid quantity of zooplankton, removing said zooplankton after saidpredetermined time period at said predetermined temperature and storingsaid zooplankton.

According to yet a further aspect of the invention, there is provided amethod of producing a feed product comprising a method of producing afeed product comprising drying a quantity of harvested zooplankton bypassing said zooplankton through a dryer, said dryer having a pluralityof moveable balls intended to contact said zooplankton at a temperaturewhich is elevated by passing a volume of preheated air through saidballs and said zooplankton at a predetermined temperature and volume fora predetermined time period.

According to yet a further aspect of the invention, there is providedapparatus to obtain a feed product from zooplankton comprising means tohold a quantity of said zooplankton, means to raise the temperature ofsaid holding means to a predetermined value, means to distribute saidpredetermined temperature throughout said quantity of zooplankton, meansto maintain said predetermined temperature for a predetermined time insaid zooplankton and means to remove said quantity of zooplankton fromsaid holding means after said predetermined time at said predeterminedtemperature.

According to a further aspect of the invention, there is provided amethod of producing a feed product comprising drying a quantity ofharvested zooplankton by passing said zooplankton through a dryer, saiddryer having a plurality of movable balls intended to contact saidzooplankton at an elevated temperature which is maintained by passing avolume of preheated air through said balls and a volume of zooplanktonfor a predetermined time period.

According to yet a further aspect of the invention, there is provideddrying apparatus for drying zooplankton comprising means to introducesaid zooplankton to a dryer container, means to introduce apredetermined flow of heated air to said dryer container thereby to heata plurality of balls movable within said container to a predeterminedtemperature and bringing said zooplankton into contact with said heatedballs for a predetermined time period.

According to yet a further aspect of the invention, there is provided amethod for producing a feed product or additive comprising the steps ofsubjecting a quantity of zooplankton to a predetermined temperature fora predetermined time period in order to maintain enzymatic activity ofsaid zooplankton enzymes to effect partial autolysis of said zooplanktonand/or other protein containing compounds that may be mixed with thehydrolysolic and thereafter suspending said enzymatic activity by dryingsaid zooplankton at a temperature less than 70° C. to preserve theplankton enzyme in said zooplankton.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Specific embodiments of the invention will now be described, by way ofexample only, with the use of drawings in which:

FIG. 1A is a diagrammatic isometric view of a fishing vessel with anattached net which utilizes the euphausiid harvesting techniqueaccording to the invention;

FIG. 1B is a diagrammatic front view of a net in an alternativeharvesting technique according to the invention;

FIG. 2A is a diagrammatic side view of a cage which is used to maintainthe cod end of the fishing net illustrated in FIG. 1 in an open positionand which is further used to transport the harvested euphausiids to theharvesting vessel;

FIGS. 2B and 2C are side and rear views, respectively, of the dewateringtrough used to remove water from the harvested euphausiids;

FIG. 3 is a diagrammatic process chart illustrating the processing ofthe euphausiids subsequent to the dewatering steps illustrated in FIG. 2and prior to the drying step;

FIGS. 4A and 4B are end and side sectional views of the heat exchangerused to raise the temperature of the harvested euphausiids prior to thedigester process;

FIG. 5 is a diagrammatic side sectional view of the digester used tocreate the desired enzyme level within the euphausiids; and

FIG. 6 is a diagrammatic side sectional view of a ball drier used to drythe euphausiids following removal of the euphausiids from the surge tanklocated downstream from the digester.

DESCRIPTION OF SPECIFIC EMBODIMENT

Referring now to the drawings, a towing vessel 10 is illustrated inFIG. 1. A plurality of towing ropes 11, 12, 13 are connected to thetowing vessel 10 in order to tow a barge 14 and a net 20. A plurality ofropes 21 (only one of which is shown) are connected to the net 20 andextend downwardly from the barge 14. Weights 22 are connected to thebottom of the open forward facing portion of the net 20 in order tomaintain the net 20 at a desired and predetermined depth where theconcentration of zooplankton is satisfactory.

The cod or rearward end 23 of the net 20 is maintained in an opencondition by the use of a cage generally illustrated at 24 in FIG. 2.Cage 24 is of cylindrical configuration and is positioned within the codend of net 20. It is made from aluminum and is preferably corrosionresistant. A fitting 30 is welded to the downstream end of the cage 24and one end of a swivel connection 31 is joined to the fitting 30 toprevent fouling the net in the event components become unstable underadverse harvesting conditions. A hose 32 is connected to the other endof the connection 31.

Referring again to FIG. 1, hose 32 extends upwardly from the cod end ofthe net 20 to the barge 14. A pump of a variety of configurations but,conveniently, a diaphragm sump pump 33, is located at the other end ofthe hose 32 on barge 14. A dewatering trough is generally shown at 34and is illustrated in FIGS. 2B and 2C. Dewatering trough 34 has alengthwise generally rectangular configuration and is also located onbarge 14. Dewatering trough conveniently takes the configuration of a"lazy L". A set of screens 40 positioned at obtuse angles are utilisedto allow water to drain from the pumped euphausiids and exit the trough34 through drain pipes 41 while the euphausiids accumulate within thedewatering trough 34.

A blast freezer 42 was also located on the barge 14 to stabilize theharvested euphausiids. The blast freezer 42 subjects the euphausiids toa temperature of approximately +9° to -17° C. and is used to freeze thedewatered euphausiids and stabilize the product for further processing.The euphausiids accumulate within the dewatering trough 34 and which areperiodically removed from the trough 34 from time to time for freezing.Thereafter, the frozen euphausiids are transported to a processinglocation and processed as described hereafter.

In prototype demonstrations, the net 20 utilised for the harvestingoperation was a specially designed 13 ft. by 21 ft. plankton netsuspended from a 46 ft. aluminum barge. The pumping action was by athree inch diaphragm pump located on the barge 14 and the freezingaction occurred within a minus seventeen (-17° C.) degree centigradeblast freezer 42.

As earlier described, the frozen euphausiids are transported to aprocessing location in order to transform the euphausiids into thedesired feed product. Reference is now made to the flow chart of FIG. 3.

A pump 43 is connected to a hopper 44 which receives the euphausiidswhich are now in a thawed condition. Pump 43 is connected to a heatexchanger generally illustrated at 50 and diagrammatically illustratedin FIG. 3. The heat exchanger 50 is intended to raise the temperature ofthe euphausiids to a temperature of approximately 40° C. to 60° C. whichwill more closely approximate the temperature maintained in the digesterwhich is generally lower than 70° C. and which digester is generallyillustrated at 51. Digester 51 is located downstream of the heatexchanger 50 in the process illustrated in FIG. 3.

Although several different types of heat exchangers may be used, heatexchanger 50 conveniently comprises a plurality of pipes 52 (FIG. 4A) inwhich the euphausiids are conveyed through the heat exchanger. Heatedwater enters the inlet 54 of the heat exchanger 50 and is circulatedthrough the heat exchanger 50 generally following the flow path seen inFIG. 4B which utilizes a plurality of baffles 53. The heated water exitsthe heat exchanger at outlet 61. Following the increase of temperaturecreated in the euphausiids by the heat exchanger 50, the euphausiidspass to the digester 51.

Digester 51 is seen is greater detail in FIG. 5. It comprises a productinlet 61 and a product outlet 62. A water inlet 63 and a water outlet 64are provided. A water jacket 70 through which the heated watercirculates surrounds the cylindrical cavity area 71 of the digester 51which contains the euphausiids. A plurality of stirring discs 72 arelocated vertically within the cavity area 71 of the digester 51 and areused to stir the euphausiids when they are positioned within thedigester 51. A valve 73 is used to close the product outlet 62 so as tomaintain the euphausiids within the digester 51 until the propertemperature and time for the desired enzyme formation within theeuphausiids has taken place. The time period has conveniently extendedbetween thirty (30) minutes and two (2) hours.

Although it is presently thought that a degree of digestibility willenhance the feed product only for certain fish such as early stagelarvae or juveniles, it is contemplated by the applicant that suchdigestibility may enhance the feed product for virtually all fish. Inutilising the digester 51 illustrated in FIG. 5, a batch process iscurrently being used with a volume of euphausiids of 250 lb./hr beingused.

The valve 62 is then opened and the quantity of euphausiids within thedigester 51 pass through the valve 62 and are transported through valve74 to the surge tank or heated batch storage vessel 80 where they awaittreatment in the dryer, conveniently a ball dryer generally illustratedat 81 (FIG. 6) where relatively low and controlled temperatures can beapplied to the euphausiids such that any enzymes existing within theeuphausiids are not inactivated as would otherwise be the case in anormal drying process.

The euphausiids pass from the storage vessel 80 to the ball dryer 81through product inlet 83 and, thence, about the periphery of the dryer81 initially through the application zones 91 where the balls initiallycontact the euphausiids and begin the drying process. The ball dryer 81performs a "soft" drying process which reduces damage to the euphausiidsbecause of its gentle action. The ball drying process utilises acontinuous feed into the ball dryer 81 and a product flow of 15 lb./hr.is available.

As the balls and euphausiids move downwardly through the drying zones92, they meet a counter-current flow of controlled-temperature dryingair at less than 50° C. which air enters the ball dryer 81 through airinlet 82. Air flow, temperature and dwell time are precisely controlledand monitored within this zone. All of these are variable factors whichdepend upon whether the product is wet or dryer and what period of timethe product is intended to stay in the dryer 81.

In the separation zone 93 at the bottom of the dryer 81, the ball andeuphausiids meet a co-current flow of controlled temperature air forfinal drying and separation. The dried euphausiids leave the ball dryer81 through the product outlet 84 and pass to the packaging step. Thedrying balls are elevated by rotating helix 94 and recycled to theapplication zone 91 and the process continues.

While one of many commercial ball dryers may be used for the air dryingof the euphausiids, an ECAL Pilot Drier Type 25F has been foundsatisfactory for the prototype purposes outlined in this application.This ball drier is produced by ECAL PDS America, Inc. of Princeton, N.Y.

It is contemplated that although the processing of the euphausiids hasbeen described as taking place at a land location, such processing stepsmay take place at the harvesting location on board either the harvestingvessel or another vessel conveniently located nearby. This results inadvantages in that the euphausiids need not be frozen followingharvesting and need not be transported to a land based processing plantthereby resulting in considerable cost savings and quality improvement.In addition, the euphausiids may be introduced directly to the balldryer 81 following harvesting. The dried euphausiids, after beingsubjected to the digester and/or the drying processes, may then bestored on the vessel until a substantial quantity have been obtained atwhich time they may be transferred to another vessel for transport tothe processing vessel itself which, when full, will transport theeuphausiids to the shore.

Likewise and while it is desirable for the digester and drying steps totake place concurrently and sequentially in the event the euphausiidsare intended to be used as a feed product for juvenile and early stagelarvae, it is further contemplated that the euphausiids may be drieddirectly following harvesting in the event the digester step is notrequired as would be the case, for example, if the harvested euphausiidsare intended to be used as a food product such as for use as an additiveor as an animal feed where pre-digestion is not required such as, forexample, when use as a cat food, for example, or as an appetizer iscontemplated.

A further harvesting technique is contemplated in FIG. 1B. In thistechnique, weights 101 are connected to the mouth end of the netgenerally illustrated at 114 at the ends of the lower horizontal beam103. Floats 100 are connected to the top horizontal beam 102 of themouth end of the net 114. Depending on the size of the net 114, linesare connected on one end to attachment points 104, in the first instanceor, alternatively, to points 110, 111, 112, 113 and, on the other end,to the towing vessel. The net 114 is pulled through the water gatheringthe zooplankton which enter the net 114 through the mouth.

Other applications for the hydrolysed krill product are alsocontemplated. Fish under stress, which is common with cultivated speciesraised with aquacultural techniques, are reluctant to eat and,accordingly, therapeutic drug delivery and special diets used for suchmarine species are difficult to use because the fish do not find suchproducts palatable. The hydrolysed krill and other zooplankton productaccording to the invention may be used with such special diets and drugdelivery by creating an enhanced flavour when the medicinal product suchas a pellet is coated or mixed with the hydrolysed zooplankton productin a liquid or paste form. Likewise, while other such products mayinclude specially added amino acids and other compounds to enhance theflavour of the product, the hydrolysed krill according to the presentinvention preserves and enhances the level of certain free amino acidsand other flavourants thereby allowing flavour enhancement with anatural product and without the addition of amino acids or otherflavourants. Likewise, the krill retain the original pigments and fattyacids. The activity of the enzymes, which are contained in the krill, isalso retained in the hydrolysed natural product according to theinvention. Such enzymes allow for enhanced digestion by cultivatedmarine species by increasing the availability of peptides and free aminoacids without creating additional harmful stress on such species.

Yet a further application contemplated by the present invention is theuse of hydrolysed krill in association with plant or vegetable proteinsuch as soymeal and canola in fish feed mixtures. Such an applicationwould increase the digestibility of the plant protein which inherentlyand by itself has relatively low digestibility and palatability. This isso because the enzymes in the hydrolysed krill products according to theinvention are preserved by the hydrolysis and act on the plant proteins.The enhanced digestibility of a product combination of plant protein andhydrolysed krill is also contemplated to reduce the fecal load in theenvironment by fish fed with such combination. This can be an importantfeature with cultivated marine and freshwater species. Likewise, thepalatability of such non-fish meal proteins, in particular, plantproteins such as canola or soy meal, is enhanced.

Experiments conducted to date utilize the enzymes in krill to carry outa limited hydrolysis of canola and other plant proteins. For example,one part of dry canola or soy meal which has added ten percent (10%)wheat bran is blended with five (5) parts of hydrolysed krill. Thehydrolysate is pumped from the digester to the feed stock hopper and thedry blend is added. The mixture is brought to the desired temperatureand agitated in the digester for approximately one (1) hour.Measurements of phytic acid and the levels of the amino acids andammonia are then taken. For example, 250 lbs. of krill is hydrolysed bybringing the krill to approximately 45° Celsius. The temperature is heldfor one (1) hour and is then blended with 5 lbs. of wheat bran with 45lbs. of canola concentrate. The use of wheat bran is necessary toprovide phytose, an enzyme which is absent in canola meal and krill. Thephytic acid is dephosphoiyloted by phytose from the wheat bran. Thephytic acid is acted on by the enzymes. It is noted that the blend maybe retained in the digester for an extended period, up to a period offour (4) hours or even longer.

While specific embodiments of the invention have been described, suchdescription should be taken as illustrative of the invention only andnot as limiting its scope as defined in accordance with the accompanyingclaims.

We claim:
 1. A method of harvesting zooplankton comprising towing atrawl net behind a vessel in coastal waters through a location ofzooplankton and above the bottom of said coastal waters, said net beingflexible and having an open forward end and a rearward cod end to gathersaid zooplankton, a first member to maintain said open end of said netat a predetermined depth below the surface of said coastal waters wheresaid zooplankton are located, a cage in said cod end of said net tomaintain said cod end of said net in an open condition, said case havingan inlet for ingesting said zooplankton gathered by said net at the mostrearwardly positioned location of said cage such that said zooplanktonflow smoothly rearwardly through said net and cage and into said inletand a pump operably connected to said cod end of said flexible net tocontinuously remove said zooplankton from said cod end of said flexiblenet to a shipboard location.
 2. A method of harvesting zooplankton as inclaim 1 and further comprising dewatering said zooplankton at saidshipboard location.
 3. A method of harvesting zooplankton as in claim 2and further comprising freezing said dewatered zooplankton.
 4. A methodof harvesting zooplankton as in claim 1 wherein said zooplanktoncomprise euphausiids.
 5. Apparatus for harvesting zooplankton fromcoastal waters comprising a flexible trawl net having an open end and arearward cod end, a new tow device to pull said net behind a towingvessel above the bottom surface of said coastal waters, first members tomaintain said open end of said trawl net at a predetermined depth belowthe surface of said coastal waters, a cage at said cod end of said netto maintain said cod end of said net in an open configuration and a pumpto pump said zooplankton from said cod end of said net to a shipboardlocation through a flow member, said flow member having a suction end insaid cage, said zooplankton flowing rearwardly through said net and cageand into said suction end of said flow member without essential forwardor rotational movement.
 6. Apparatus for harvesting zooplankton as inclaim 5 wherein said pump is a diaphragm pump.
 7. Apparatus forharvesting zooplankton as in claim 5 and further comprising a dewateringdevice to dewater said zooplankton at said shipboard location. 8.Apparatus for harvesting zooplankton as in claim 7 and furthercomprising a freezing device to freeze said zooplankton at saidshipboard location.
 9. Apparatus for harvesting zooplankton as in claim5 wherein said zooplankton comprise euphausiids.